Mold for chromium alloys



Patented Feb. 10, 1925.

f- UN TE T TESPATE OF -w'E-T WILLIAM E. SMITH, or CLEVELAND; ND CHARLES M. CAMPBELL, or nAs'r C EvE.

LAND, onro, AssmNonsc'ro PIONEER ALLoY rnonuors COMPANY,- or CLEVE- LAND, O'HIO, A CORPORATION or DELAWARE.

MOLD son. CHROMIU ALLoYs.

No Drawing.

To all whom 2'2? may concerm v v I Be 1t known that we, IVILLrAjM'H". SMITH and CHAnLnsM. CAMPBELL, citizens "of the United States, residing. respectively, at

5 Cleveland and'East' Cleveland. inthe county of Cuyahoga and State of Ohio, have invented certain new and useful Improvements in Molds for Chromium Alloys, of which the following is a specification.

1 This invention relates to the casting of high chromium alloys and has for its object the provision of a new and improved mold wherein accurate castings can be made without contaminating the alloy. It is known that alloys of chromium with iron group metals are very diflicult to cast especially if the proportionof chromium be high and the carbon low. At the elevated temperature required to effect complete fusion of such an alloy, the chromium reacts upon silica, with absorption of silicon and the production of silicon and the production of frothing and blow-holes. The object of our invention is the provision of a mold material which shall produce smooth and regular castings; which shall not materially shrink or expand either up on drying or heating; which shall be made by exactly the same processes as in standard foundry practice, thus avoiding special training of workmen; which shall be capable of being used over and over again like ordinary sand; while further objects and advantages of the invention will become apparent as the description proceeds. In the performance of our invention we employ magnesite as the primary. mold material. This material possesses a brittleand somewhat porous nature, and upon crush- I ing ordinarily produces irregular, jagged particles which when packed together asin the making of a mold produce such a dense and interlocked mass as to be substantially non-porous, especially when mixed with the necessary binder to hold the grains in fixed relation with each other. In order to produce a successful mold by the use of this material we find it necessary first to reduce the particles toa rounded granular shape which shall enable them to be packed together in a solid relation without at the same time producing a non-porous mass. At the same time we have found i-tdesirable to produce uniformly graded mixture Application filed September 11, Serial No.' 58"t':,57 3.

"containing gra'inspf difiere'nt .sizes'j'which "shall produce a solid mass desplte the elimination'of the agged interlocking'corners.

. In the performance ofour said invention werrush this magneslte to a fineness dependent upon the size of the molds which are to be made. Formoldsof approximate- 1y a foot square We find it well to crush the material until all of the same "will pass a screen of 16 mesh. The crushed material is then tumbled or rumbled together so that the particles may become rounded by mutual attrition and screened to fineness of say 16 mesh, 20 mesh, 32 mesh and finer. These different finenesses are then mixed together in the proportions of say twenty-five per cent of sixteen mesh, twenty-five per cent of twenty mesh, and the balance thirty-two mesh and finer, care being taken not unduly to break the particles. With these we mix a certain proportion of suitable binding material, for. example two per cent more or less of clay (either fire clay or common clay) and two per cent more or less of av starchy material such as corn flour. This mixture is then tempered with water to the desired consistency'and packed into molds according to the usual foundry practice. These molds are then baked in a suitable oven to drive off excess mositure owing to the very high temperature of the molten metal, thereby producing a mold of the desired mechanical strength and internal smoothness combined with the desired porosity toenable the ready escape of air and mold gases.

After the metal is poured the casting is removed in the usual manner and the mold material is left in a friable lumpy condition. The lumps are broken down to the original grain size by rumbling. It is also ordinarily desirable to screen the material and re-prepare a graded mixture since the handling will have reduced such a proportion. of the same to dust thatvnot all can be reused. p

The larger the, molds the larger can be the sizes of the grains.

Having thus described our invention what we claim is: p

'1. A mold for chromium alloys wherein the metal contacting surfaces consist substantially of magnesite.

2. A mold for chromium containing a1-v loys made essentially of crushed magnesite and a binder.

3. A mold for chromium containing alloys made essentially of crushed magnesite mixed with a' small portion of clay.

4. A mold for chromium-containing alloys made essentially of crushed magnesite, clay, and starchy material.

5. A mold for chromium containing alloys made of a graded mixture of rounded grains ofaoid-free, basic material having the herein essential properties of magnesite 'mixed'with sufiioient binder to hold the grains together Without overcoming th porosity of the mass." 5

6. A COIIIEOSltlOH of matter for making] moldsfor c omium containing alloys, consisting essentially of a graded 'mixture of rounded grains of magnesite mixed 'with a small proportion of binding material.

7. Process of producing molds for chrorniurn containing alloys which contains the steps of crushing magnesite to granular form rumbling the grains to round their 4 corners, adding a suitable binder, andtamp- :ing into molds.

tamping the mixture into molds, and dryour signatures.

WILLIAM H. SMITH. CHARLES M. CAMPBELL.

In testimony whereof, we hereunto 'aflix, 

